The invention relates to devices for mixing and degassing a flowable mass, and particularly to devices for degassing a casting resin containing a filler.
A mixing and degassing device of the type mentioned has been described in U.S. Pat. No. 5,833,363. This device is provided with a cylindrically constructed, evacuatable container, the container axis of which is oriented essentially in a vertical direction, and a shaft extending along the container axis and having agitation arms and a distribution plate. A flowable, gas-containing mass, for example a filler-containing casting resin, is guided inside this device under the force of gravity and under agitation from a storage space on the top by way of a thin layer degassing system that removes the gas from the flowable mass into a buffer space provided at the bottom of the container, in which buffer space the degassed mass is temporarily stored under agitation. For the degassing, the flowable mass is guided first in the form of thin layers over the rotating distribution plate and is further passed from there via suitably arranged baffle plates and slots to the heating coils of the thin layer degassing system. Since the mass to be degassed flows primarily in a vertical direction and in layers of varying thickness through the degassing system, the degassing may not take place evenly.
It is an object of this invention to provide a device for producing a degassed mass that is characterized by a high degree of homogeneity. Such a device is used to prepare a castable mass just before the mass is poured into molds inside a casting apparatus. The mass is effectively degassed and mixed inside this device. This eliminates undesirable gas inclusions in the mass to be cast and a demixing of the mass, for example by sedimentation in a filler-containing casting resin.
In the mixing and degassing device according to the invention, the mass to be degassed flows primarily in thin layers, and primarily at a constant speed, from top to bottom through the thin layer degassing system. Because of this, and because the staying time of the mass to be degassed on the thin layer degassing system can be substantially modified by the number and slope of conical run-off surfaces, an extremely homogeneous degassed mass is produced. By deflecting the mass to be degassed at the ends of the conical run-off surfaces, the layers vary in their thicknesses. This results in a natural circulation of the layers and significantly improves the homogeneity of the degassed mass.
It is especially advantageous if the thin layer degassing system is provided with at least one stripping element located just above one of the two run-off surfaces. This stripping element on the one hand produces a mass layer of even thickness. This layer can be degassed quickly and safely, even for highly viscous masses. On the other hand, the stripping element hereby intensively swirls the mass to be degassed by smoothing it and stripping it off and in this way ensures that the components of the mass remain well mixed. Any sedimentation of the mass, even during long staying times in the thin layer degassing system, is avoided in this way. At the same time, as a result of the turbulent mixing, the stripping element, which also acts as an agitating element, ensures quick heating, i.e., a quick heat transfer from the heatable run-off surface to the mass layer. Since practically only thin layers are degassed, it is prevented that during the degassing well degassed and less well degassed masses mix, and in this way an especially advantageous, homogeneous mass is formed for further processing.